The present invention relates to a high-pressure gas laser apparatus and a method of processing with laser, or more in particular to a high-pressure laser apparatus suitable for excimer laser of large aperture (beam size) and high output power and a method of processing using laser.
A method using a corona UV preionization described in CLEO' 88, p. 64 is well known as a conventional technique for enlarging the aperture of the discharge-pumped excimer laser. According to this method, after application of a voltage between main electrodes, a certain lead time is inserted before generating a corona discharge on one of the main electrodes, and the UV light contained in the discharge is used to cause preionization of the main discharge space thereby to start main discharge with trigger action.
In the above-mentioned prior art system, which utilizes the UV light caused with the corona discharge for preionization, it is easy to increase the aperture (diameter) of discharge along the width of the electrodes in the main discharge space in principle. Since the attainment of uniform discharge along the electrode gap is limited, however, it is impossible to generate a laser beam of large.
JP-A-63-199475 discloses a method of preliminary ionization of a gas laser apparatus which is so configured that an X ray from an X-ray tube is used as a source of preionization of a discharge-pumped excimer laser and the X ray is irradiated from the back side of cathode of porous opening structure among the main discharge electrodes.
On the other hand, a system using a laser beam as a source of preionization is disclosed in U.S. Pat. No. 4,679,203. This system is such that a laser beam for preionization is irradiated between main discharge electrodes to attain preionization while at the same time energizing a rail gap switch at a time point when the pulse voltage of a pulse forming line circuit (PFL) indicates a crest value.